Doss S K
J Dent Res. 1976 Nov-Dec;55(6):1067-75. doi: 10.1177/00220345760550061001.
The zeta potential of hydroxyapatite (HA) at a constant pH depends on the type of acid used. Fluoride ions increase the charge density and make the surface less prone to attack by acid or alkali. Sn2+ and Th4+ ionic complexes with fluoride ions and increase the uptake of fluoride by HA.